With respect to a vehicle in which an engine is mounted, there has been known an automatic transmission that automatically, optimally sets a transmission ratio between the engine and driving wheels, as a transmission to appropriately transmit torque and revolution generated by the engine to the driving wheels in accordance with driving conditions for the vehicle.
There has been known a belt type continuously variable transmission (CVT: Continuously Variable Transmission) that continuously adjusts the transmission ratio as an automatic transmission mounted in the vehicle and the like (for example, see patent document 1 and patent document 2).
FIG. 9 shows one example of a belt type continuously variable transmission. The belt type continuously variable transmission 500 of this example includes a primary pulley 501 on an input side thereof, a secondary pulley 502 on an output side thereof, and a belt 503 around which the primary pulley 501 and the secondary pulley 502 are wound.
The primary pulley 501 is a variable pulley whose effective diameter is variable, and is constituted of a stationary sheave 511 integrally provided with a primary shaft 510, and a movable sheave 512 that is arranged slidably only in the axial direction of the primary shaft 510. Similarly, the secondary pulley 502 is a variable pulley whose effective diameter is variable and is constituted of a stationary sheave 521 integrally provided with a secondary shaft 520, and a movable sheave 522 that is arranged slidably only in the axial direction of the secondary shall 520.
On the side of the movable sheave 512 of the primary pulley 501, there is provided an oil actuator 513 to change a V-groove width between the stationary sheave 511 and the movable sheave 512. Also, on the side of the movable sheave 522 of the secondary pulley 502, there is provided an oil actuator 523 to change a V-groove width between the stationary sheave 521 and the movable sheave 522.
With respect to the belt type continuously variable transmission 500 of the configuration described above, by controlling oil pressure of the oil actuator 513 of the primary pulley 501, each V-groove width of the primary pulley 501 and the secondary pulley 502 is varied, and a winding diameter (effective diameter) of the belt 503 is varied, whereby successively changing the transmission ratio. Also, the oil pressure of the oil actuator 523 of the secondary pulley 502 is controlled in such a manner that the belt 503 is clamped under predetermined clamping pressure that does not cause belt slippage.
In a belt type continuously variable transmission 4 shown in FIG. 9, the primary shaft 510 is rotatably supported by two bearings 541 and 542. The bearing 541 on the outer side of the stationary sheave 511, out of the two bearings 541 and 542, is held by a transaxle case 506, and the bearing 542 on the outer side of the movable sheave 512 is held by a transaxle rear cover 507.
Also, one end portion of the secondary shaft 520 is rotatably supported by a bearing 551 held by the transaxle rear cover 507 on the outer side with respect to the stationary sheave 521, and the other end portion of the secondary shaft 520 is rotatably supported by a bearing 522 disposed on the outer side with respect to the movable sheave 522. Further, in the stationary sheave 521 of the secondary pulley 502, a parking gear 508 is integrally provided at the outer circumferential portion on the side of the bearing 551.